Description

Mixed Laminaria hyperborea and Laminaria ochroleuca forest on upper infralittoral moderately exposed or sheltered rock is restricted to the coast of Cornwall and the Isles of Scilly. Unlike L. hyperborea, however, L. ochroleuca has a smooth stipe and it lacks the epiphytic growth of seaweeds. The bryozoan Membranipora membranacea may encrust the very lower part of the stipe but the rest of the stipe is characteristically bare. The fronds too are generally free of encrusting hydroids, bryozoans and grazing gastropods as compared to L. hyperborea. L. ochroleuca holdfasts, however, are often encrusted with sponges and colonial ascidians. A large variety of foliose and filamentous red seaweeds are often present underneath the canopy. These include Callophyllis laciniata, Plocamium cartilagineum, Cryptopleura ramosa, Delesseria sanguinea, Dilsea carnosa Bonnemaisonia asparagoides, Erythroglossum laciniatum, Sphaerococcus coronopifolius, Polyneura bonnemaisonii and Corallina officinalis. The foliose brown seaweed Dictyota dichotoma is frequently found in this biotope along with the occasional kelp such as Saccorhiza polyschides and Saccharina latissima. The faunal composition of the biotope as a whole is often sparse. The anthozoans Corynactis viridis and Caryophyllia smithii are common on vertical surfaces with scattered bryozoan turf species such as Crisiidae. Grazers such as the gastropod Gibbula cineraria and the urchin Echinus esculentus are often present. L. ochroleuca occurs across a wide range of wave exposures (in common with L. hyperborea) and consequently it occurs at low abundance in other kelp biotopes (sheltered through to exposed) that occur in the South-West between Dorset to Lundy. In such cases, records should be considered as regional variations of the usual kelp biotopes. Records should only be assigned to this biotope when the canopy is dominated by L. ochroleuca alone, or by a mixture of both L. hyperborea and L. ochroleuca (though the latter is usually at greater abundance). L. ochroleuca commonly occurs on the Brittany and Normandy coasts.

Depth range

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Additional information

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Further information sources

Sensitivity characteristics of the habitat and relevant characteristic species

IR.LIR.K.LhypLoch is characterized by mixed canopies of Laminaria hyperborea and Laminaria ochroleuca, where Laminaria ochroleuca is the dominant or most abundant kelp. IR.LIR.K.LhypLoch is limited to the south west coast of England and recorded in moderate to sheltered wave exposed environments (Connor et al., 2004). Beneath the kelp canopy is an understory dominated by red seaweeds which include Plocamium cartilagineum, Cryptopleura ramosa and Callophyllis laciniata.

Laminaria ochroleuca is a traditionally Lusitanian kelp species which was first recorded in the UK in the Hamble Estuary in 1948 (Parke, 1948), however, has since spread east to the Isle of Wight and North to Lundy Island (Blight & Thompson, 2008; Brodie et al., 2009). Laminaria ochroleuca is morphologically similar to Laminaria hyperborea but lacks the epiphytic stipe growth (Smale et al., 2014). At the time of writing relatively little is known on the ecological effects or growth of Laminaria ochroleuca in the UK (Smale et al., 2014). In general however, kelp beds increase the three-dimensional complexity of unvegetated rock (Birkett et al., 1998b; Norderhaug, 2004; Norderhaug et al., 2007; Norderhaug & Christie, 2011; Gorman et al., 2012 ; Moy & Christie 2012; Smale et al., 2013), and support high local diversity, abundance and biomass of epibenthic species (Smale et al., 2013), and serve as nursery grounds for a number of commercial important species, e.g. Cod and Pollack (Rinde et al., 1992).

In undertaking this assessment of sensitivity, an account is taken of knowledge of the biology of important characterizing species in the biotope. There is an abundance of literature for regeneration of mono-specific Laminaria hyperborea beds, however at the time of writing, there is limited research for the recovery of mixed kelp canopies and specifically Laminaria ochroleuca growth and recovery within the UK. For this sensitivity assessment Laminaria hyperborea and, in particular, Laminaria ochroleuca are the primary foci of research. The abundance of Laminaria ochroleuca is important for to the recognition of this biotope (important characterizing) and a decrease in its abundance will probably result in loss of the biotope and its replacement by another kelp biotope. The understory red seaweed communities also characterize the biotope but are present in other Laminaria biotopes, and are therefore not a primary focus of research. Examples of important species groups are mentioned where appropriate.

Resilience and recovery rates of habitat

Laminaria ochroleuca is a Lusitanian kelp species which has a geographic range from the Messina strait in the Mediterranean to its northern limit in the south west of the UK (Smale et al., 2014). Laminaria ochroleuca is most abundant in wave sheltered locations (John, 1971; Yesson et al., 2015), however, surveys in 2013-14 found Laminaria ochroleuca to be common in moderately exposed locations of Plymouth Sound, UK. In Portugal Laminaria ochroleuca’s reproductive season lasts from April-May to November-December (when sori become visible, Pereira et al. (2011). Laminaria spp. recruitment has been shown to be highly seasonally specific, and the survival of various growth phases to be temperature dependent (Birkett et al., 1998), therefore Laminaria ochroleuca reproduction times could differ across its distribution range, specifically in the UK. At the time of writing there is limited information on the reproduction and life history of Laminaria ochroleuca (Barradas et al., 2011). However, Laminaria ochroleuca is very similar to Laminaria hyperborea and therefore (barring temperature related differences mentioned below), reproduction and recruitment processes are assumed to be similar across the two species (Birkett et al., 1998; Smale et al., 2014). Laminaria ochroleuca has a reported temperature optimum for spore development of between 12 and 18°C (Izquierdo et al., 2002). Laminaria ochroleuca spores have a maximum development temperature of 23-24°C and Pereira et al. (2011) suggested temperatures above 25°C would likely cause high mortality. When compared to other kelp species (e.g. Saccorhiza polyschides) Laminaria ochroleuca has a relatively low fecundity at 10°C. This evidence plus recent modelling (Yesson et al., 2015) suggests that Laminaria ochroleuca’ northern spread may be limited by winter temperatures and that the species may be maladapted to the environmental conditions in the UK.

In Portugal Laminaria ochroleuca has been shown to re-establish rapidly following physical removal. Barradas et al. (2011) scraped all macroalgae from intertidal rock pools, including the dominant canopy forming Laminaria ochroleuca and understory algae. Laminaria ochroleuca recruits appeared one month following removal small (mean length 2.02cm) at a mean density of 40 recruits per m2. Sporophytes had an average length of 14.91cm four months after removal and average densities of 82 recruits per m2. Barradas et al. (2011) noted a lack of recruitment in natural adjacent Laminaria ochroleuca populations and theorised that the rapid colonization of Laminaria ochroleuca was caused by latent microscopic spores on the underlying rock which grew rapidly when the Laminaria ochroleuca canopy was removed. Barradas et al. (2011) did not comment on the length of time for Laminaria ochroleuca to reach a similar size and density to that of pre-treatment nor the likely environmental conditions that spores could tolerate and for how long, however, the results in Barradas et al. (2011) demonstrate Laminaria ochroleuca can recover from disturbance rapidly.

If environmental conditions are favourable Laminaria hyperborea can recover following disturbance events reaching comparable plant densities and size to pristine Laminaria hyperborea beds within 2-6 years (Kain, 1979; Birkett et al., 1998; Christie et al., 1998). Holdfast communities may recover in 6 years (Birkett et al., 1998). Full epiphytic community and stipe habitat complexity regeneration requires over 6 years to recover (possibly 10 years) (Svendsen, 1972). These recovery rates were based on discrete kelp harvesting events and recurrent disturbance occurring frequently within 2-6 years of the initial disturbance is likely to lengthen recovery time (Birkett et al., 1998, Burrows et al., 2014). Kain (1975) cleared sublittoral blocks of Laminaria hyperborea at different times of the year for several years. The first colonizers and succession community differed between blocks and at what time of year the blocks were cleared however within 2 years of clearance the blocks were dominated by Laminaria hyperborea.

Laminaria hyperborea has a heteromorphic life strategy. A vast number of zoospores (mobile asexual spores) are released into the water column between October-April (Kain & Jones, 1964). Zoospores settle onto rock substrata and develop into dioecious gametophytes (Kain, 1979) which, following fertilization, develop into sporophytes and mature within 1-6 years (Kain, 1979; Fredriksen et al., 1995; Christie et al., 1998). Laminaria hyperborea zoospores have a recorded dispersal range of approx. 200 m (Fredriksen et al., 1995). However zoospore dispersal is greatly influenced by water movements, plus zoospore density and the rate of successful fertilization decreases exponentially with distance from the parental source (Fredriksen et al., 1995). Hence, recruitment following disturbance can be influenced by the proximity of mature kelp beds producing viable zoospores to the disturbed area. (Kain, 1979, Fredriksen et al., 1995).

Reports of large scale urchin barrens within the North East Atlantic are generally limited to regions of the North Norwegian and Russian Coast (Rinde & Sjøtun, 2005, Nourderhaug & Christie, 2009). Within the UK, urchin grazed biotopes (IR.MIR.KR.Lhyp.GzFt/Pk, IR.HIR.KFaR.LhypPar, IR.LIR.K.LhypSlat.Gz & IR.LIR.K.Slat.Gz) are generally localised to a few regions in North Scotland and Ireland (Smale et al., 2013; Stenneck et al., 2002; Norderhaug & Christie 2009; Connor et al., 2004). IR.MIR.KR.Lhyp.GzFt/Pk, IR.HIR.KFaR.LhypPar, IR.LIR.K.LhypSlat.Gz & IR.LIR.K.Slat.Gz are characterized by a canopy-forming kelp however urchin grazing decreases the abundance and diversity of understory species. In the isle of Man Jones & Kain (1967) observed low Echinus esculentus grazing pressure can control the lower limit of Laminaria hyperborea in the and remove Laminaria hyperborea sporelings and juveniles. Urchin abundances in “Urchin Barrens” have been reported as high as 100 individuals/m2 (Lang & Mann, 1976), Kain (1967) reported urchin abundances of 1-4/m2 within experimental plots of the Isle of Man. Therefore, while “Urchin Barrens” are not presently a large scale issue within the UK, relatively low urchin grazing has been found to control the depth distribution of Laminaria hyperborea, negatively impact on Laminaria hyperborea recruitment and reduce the understory community abundance and diversity.

Resilience assessment. Little is known on the recovery of Laminaria ochroleuca in the UK. Due to the similarity between Laminaria ochroleuca & Laminaria hyperborea it is assumed that the two species would have similar recovery rates. The evidence suggests that Laminaria hyperborea beds can regenerate from disturbance within a period of 1-6 years, and the associated community within 7-10 years. Therefore, resilience has been assessed as Medium from either a loss of abundance (e.g. ‘Low’ resistance) or removal of the canopy (e.g. resistance is ‘None’).

Hydrological Pressures

Of the two kelp species which define IR.LIR.K.LhypLoch, Laminaria hyperborea has a northern distribution (Birkett et al., 1998b). Laminaria ochroleuca has a southern distribution. Hence, increases in temperature above a threshold will cause an increase in the dominance of Laminaria ochroleuca.

Kain (1964) stated that Laminaria hyperborea sporophyte growth and reproduction could occur within a temperature range of 0-20°C. Upper and lower lethal temperatures have been estimated at between 1-2 °C above or below the extremes of this range (Birkett et al., 1988). Above 17°C gamete survival is reduced (Kain, 1964 & 1971) and gametogenesis is inhibited at 21°C (Dieck, 1992). It is therefore likely that Laminaria hyperborea recruitment will be impaired at a sustained temperature increase of above 17°C. Sporophytes can tolerate temperatures of 20°C (Kain, 1964). Temperature tolerances for Laminaria hyperborea are also seasonally variable and temperature changes are less tolerated in winter months than summer months (Birkett et al., 1998b).

Laminaria ochroleuca is distributed from Messina, Mediterranean to the south of the UK, and has a thermal optimum for spore development between 12-18°C (Izquierdo et al., 2002). Laminaria ochroleuca spores have a maximum development temperature of 23-24°C and temperatures above 25°C will likely cause high mortality (Pereira et al., 2011).

Subtidal red algae are less tolerant of temperature extremes than intertidal red algae, surviving between -2°C and 18-23 °C (Lüning 1990; Kain & Norton, 1990). Temperature increase may affect growth, recruitment or interfere with reproduction processes. For example, there is some evidence to suggest that blade growth in Delesseria sanguinea is delayed until ambient sea temperatures fall below 13°C. Blade growth is also likely to be intrinsically linked to gametangia development (Kain, 1987), maintenance of sea temperatures above 13°C may affect recruitment success.

IR.LIR.K.LhypLoch is recorded exclusively in the UK south west, where summer Sea Temperature (ST) range from 12-16°C, and winter 8-13°C (Plymouth: 1981-2010, Beszczynska-Möller & Dye, 2013). Little evidence is available for acute heat shock in the both Laminaria ochroleuca and Laminaria hyperborea, however, any increases in sea temperature are likely to favour Laminaria ochroleuca which has higher temperatures optimums. All temperature effects would be seasonally variable, and more affective in winter. However, an increase in 5°C in the UK south west would likely affect Laminaria hyperborea recruitment processes and limit Laminaria hyperborea sporophyte growth (Plymouth: 1981-2010, Beszczynska-Möller & Dye, 2013).

Sensitivity assessment. A long-term increase in temperature may benefit the biotope and cause a localised increase in the abundance of Laminaria ochroleuca. However, beneficial effects of pressures are not assessed. Laminaria hyperborean may decrease in abundance however IR.LIR.K.LhypLoch would still be the recognised biotope. Therefore resistance is assessed a ‘High’, so that resilience is therefore ‘High ‘and the biotope is regarded as ‘Not sensitive’ to this pressure.

Of the two kelp species which define IR.LIR.K.LhypLoch, Laminaria hyperborea has a northern distribution (Birkett et al., 1998b). Laminaria ochroleuca has a southern distribution. Hence, decreases in temperature will likely benefit Laminaria hyperborea.

Laminaria hyperborea is a boreal northern species with a geographic range from mid-Portugal to Northern Norway (Birket et al., 1998). Kain (1964) stated that Laminaria hyperborea sporophyte growth and reproduction could occur within a temperature range of 0-20°C. Upper and lower lethal temperatures have been estimated at between 1-2°C above or below the extremes of this range (Birkett et al., 1988).

Laminaria ochroleuca has a reported temperature optimum for spore development between 12-18°C (Izquierdo et al., 2002), Laminaria ochroleuca gametophyte development can occur in temperatures as low 5°C (Lüning, 1990). Recent modelling has also predicted winter temperature in the UK to strongly influence the distribution, and hence spread, of Laminaria ochroleuca in the UK (Yesson et al., 2015). Pereira et al. (2011) examined the development of early Laminaria ochroleuca life stages and found that Laminaria ochroleuca had relatively low fecundity at 10°C and may be maladapted to environmental conditions within the UK and vulnerable to local extinctions.

Subtidal red algae are less tolerant of temperature extremes than intertidal red algae, surviving between -2°C and 18-23 °C (Lüning 1990; Kain & Norton, 1990). Temperature increase may affect growth, recruitment or interfere with reproduction processes. For example, there is some evidence to suggest that blade growth in Delesseria sanguinea is delayed until ambient sea temperatures fall below 13 °C. Blade growth is also likely to be intrinsically linked to gametangia development (Kain, 1987), maintenance of sea temperatures above 13 °C may affect recruitment success.

IR.LIR.K.LhypLoch is recorded exclusively in the UK south west, where the average Sea Temperature (ST) range from 12-16°C, and winter 8-13°C (Plymouth: 1981-2010, Beszczynska-Möller & Dye, 2013). Little evidence is available for an acute cold shock in the both Laminaria ochroleuca and Laminaria hyperborea. A decrease of 5°C for 1 month during winter could negatively affect Laminaria ochroleuca fecundity, spore and gametophyte development and hence recruitment success. A decrease of 2°C for 1 year could negatively affect fecundity and spore development. A decrease in temperature may cause local extinctions of Laminaria ochroleuca and/or increase the dominance of either monospecific Laminaria hyperborea (as in IR.MIR.KR.Lhyp) or mixed Saccharina latissima canopies (IR.LIR.K.LhypSlat), dependant on the wave exposure.

Sensitivity assessment. Resistance to the pressure is considered ‘None’, and resilience ‘Medium’. The sensitivity of this biotope to a decrease in temperature has been assessed as ‘Medium’.

Lüning (1990) suggest that “kelps” are stenohaline, their general tolerance to salinity as a phenotypic group covering 16 - 50 psu over a 24 hr period. Optimal growth probably occurs between 30-35 psu (MNCR category- 'Full' salinity) and growth rates are likely to be affected by periodic salinity stress. Birkett et al, (1998) suggested that long-term increases in salinity may affect Laminaria hyperborea growth and may result in loss of affected kelp, and, therefore, loss of the biotope.

Laminaria ochroleuca grows in the Messina strait, Mediterranean where ambient salinity has been measured at 38.5‰ (Sheppard et al., 1978). Laminaria ochroleuca has also been found growing in Portuguese intertidal rock pools (Barradas et al., 2011). As a result of high evaporation rates, rainfall and land run-off, rock pools and the organisms that reside within them are likely to experience short-term high variability in salinity (Reed & Russell, 1978). The effects of long-term (e.g. ≥ 1 year) salinity changes on Laminaria ochroleuca are unknown.

Sensitivity assessment. Resistance has been assessed as ‘Low’, resilience as ‘Medium’. The sensitivity of this biotope to an increase in salinity has been assessed as ‘Medium’.

Lüning (1990) suggest that “kelps” are stenohaline, their general tolerance to salinity as a phenotypic group covering 16 - 50 psu over a 24 hr period. Optimal growth probably occurs between 30-35 psu (MNCR category- 'Full' salinity) and growth rates are likely to be affected by periodic salinity stress. Birkett et al, (1998) suggested that long-term increases in salinity may affect Laminaria hyperborea growth and may result in loss of affected kelp, and, therefore, loss of the biotope.

Hopkin & Kain (1978) tested Laminaria hyperborea sporophyte growth at various low salinity treatments. The results showed that Laminaria hyperborea sporophytes grew normally at 19 psu, was reduced at 16 psu and did not occur at 7 psu. Laminaria ochroleucaA decrease in one MNCR salinity scale from Full Salinity (30-40 psu) to Reduced Salinity (18-30 psu) may result in a decrease of Laminaria hyperborea sporophyte growth. Laminaria hyperborea may also be out-competed by low salinity tolerant species e.g. Saccharina latissima (Karsten, 2007).

Sensitivity assessment. Resistance has been assessed as ‘Low’ resilience as ‘Medium’. The sensitivity of this biotope to a decrease in salinity has been assessed as ‘Medium’.

Sensitivity assessment. The evidence suggests that both Laminaria ochroleuca and Laminaria hyperborea would be highly resistant to a change in peak mean spring bed velocity of 0.1-0.2 m/sec. Resistance to the pressure is considered ‘High’, and resilience ‘High’. The sensitivity has been assessed as ‘Not sensitive’.

IR.LIR.K.LhypLoch is recorded from the sublittoral fringe to the lower infralittoral. An increase in emergence will result in an increased risk of desiccation and mortality of the dominant kelp species (Laminaria ochroleuca & Laminaria hyperborea). Removal of canopy-forming kelps has also been shown to increase desiccation and mortality of the understory macroalgae (Hawkins & Harkin, 1985). Several mobile species such as sea urchins, brittle stars and feather stars are likely to move away. However, providing that suitable substrata are present, the biotope could re-establish further down the shore within a similar emergence regime to that which existed previously. Similarly, a decrease in emergence may allow the biotope to extend its extent up the shore, however, completion from other species would probably erode its lower extent.

Sensitivity assessment. Resilience has been assessed as ‘Low’. Resistance as ‘Medium’. The sensitivity of this biotope to a change in emergence is considered as ‘Medium’.

Kregting et al. (2013) measured Laminaria hyperborea blade growth and stipe elongation from an exposed and a sheltered site in Strangford Lough, Ireland from March 2009-April 2010. Wave exposure was found to be between 1.1 and 1.6 times greater between the exposed and sheltered sites. Maximal significant wave height (Hm0) was 3.67 & 2 m at the exposed and sheltered sites. Maximal water velocity (Velrms) was 0.6 & 0.3 m/s at the exposed and sheltered sites. Despite the differences in wave exposure and water velocity, there was no significant difference in Laminaria hyperborea growth between the exposed and sheltered site.

Biotope structure is, however, different between wave exposed and sheltered sites. Pederson et al., (2012) observed Laminaria hyperborea biomass, productivity and density increased with an increase in wave exposure. At low wave exposure, Laminaria hyperborea canopy forming plants were smaller, had lower densities and had higher mortality rates than at exposed sites. At low wave exposure high epiphytic loading on Laminaria hyperborea was theorised to impair light conditions, nutrient uptake, and increase the drag of the host Laminaria hyperborea during extreme storm events.

Sensitivity assessment. While wave exposure is a defining feature of IR.LIR.K.LhypLoch, the benchmark level of change is unlikely to have a significant effect in areas already subject to wave exposure, even where sheltered. Resistance has been assessed as ‘High’, resilience as ‘High’. Sensitivity has been assessed as ‘Not Sensitive’.

Chemical Pressures

This pressure is Not assessed but evidence is presented where available.

Bryan (1984) suggested that the general order for heavy metal toxicity in seaweeds is: Organic Hg > inorganic Hg > Cu > Ag > Zn > Cd > Pb. Cole et al. (1999) reported that Hg was very toxic to macrophytes. Similarly, Hopkin & Kain (1978) demonstrated sub-lethal effects of heavy metals on Laminaria hyperborea gametophytes and sporophytes, including reduced growth and respiration. Sheppard et al. (1980) noted that increasing levels of heavy metal contamination along the west coast of Britain reduced species number and richness in holdfast fauna, except for suspension feeders which became increasingly dominant. Gastropods may be relatively tolerant of heavy metal pollution (Bryan, 1984). Echinus esculentus recruitment is likely to be impaired by heavy metal contamination due to the intolerance of its larvae. Echinus esculentus are long-lived and poor recruitment may not reduce grazing pressure in the short-term. Although macroalgae species may not be killed, except by high levels of contamination, reduced growth rates may impair the ability of the biotope to recover from other environmental disturbances.

This pressure is Not assessed but evidence is presented where available.

Laminaria hyperborea and Laminaria ochroleaca fronds, being almost exclusively subtidal, would not come into contact with freshly released oil, but only to sinking emulsified oil and oil adsorbed onto particles (Birket et al., 1998). The mucilaginous slime layer coating of laminarians may protect them from smothering by oil. Hydrocarbons in solution reduce photosynthesis and may be algicidal. However, Holt et al. (1995) reported that oil spills in the USA and from the Torrey Canyon had little effect on kelp forests. Similarly, surveys of subtidal communities at a number sites between 1-22.5 m below chart datum, including Laminaria hyperbora communities, showed no noticeable impacts of the Sea Empress oil spill and clean up (Rostron & Bunker, 1997). An assessment of holdfast fauna in Laminaria showed that although species richness and diversity decreased with increasing proximity to the Sea Empress oil spill, overall the holdfasts contained a reasonably rich and diverse fauna, even though oil was present in most samples (Somerfield & Warwick, 1999). Laboratory studies of the effects of oil and dispersants on several red algae species, including Delesseria sanguinea (Grandy 1984; cited in Holt et al., 1995) concluded that they were all sensitive to oil/dispersant mixtures, with little differences between adults, sporelings, diploid or haploid life stages. Holt et al. (1995) concluded that Delesseria sanguinea is probably generally sensitive of chemical contamination. Overall the red algae are likely to be highly intolerant to hydrocarbon contamination. Loss of red algae is likely to reduce the species richness and diversity of the biotope and the understorey may become dominated by encrusting corallines; however, red algae are likely to recover relatively quickly.

This pressure is Not assessed but evidence is presented where available.

O'Brian & Dixon (1976) suggested that red algae were the most sensitive group of macrophytes to oil and dispersant contamination (see Smith, 1968). Although Laminaria hyperborea sporelings and gametophytes are intolerant of atrazine (and probably other herbicides) overall they may be relatively tolerant of synthetic chemicals (Holt et al., 1995). Laminaria hyperborea survived within >55 m from the acidified halogenated effluent discharge polluting Amlwch Bay, Anglesey, albeit at low density. These specimens were greater than 5 years of age, suggesting that spores and/or early stages were more intolerant (Hoare & Hiscock, 1974). Patella pellucida was excluded from Amlwch Bay by the pollution and the species richness of the holdfast fauna decreased with proximity to the effluent discharge; amphipods were particularly intolerant although polychaetes were the least affected (Hoare & Hiscock, 1974). The richness of epifauna/flora decreased near the source of the effluent and epiphytes were absent from Laminaria hyperborea stipes within Amlwch Bay. The red alga Phyllophora membranifolia was also tolerant of the effluent in Amlwch Bay. Smith (1968) also noted that epiphytic and benthic red algae were intolerant of dispersant or oil contamination due to the Torrey Canyon oil spill; only the epiphytes Crytopleura ramosa and Spermothamnion repens and some tufts of Jania rubens survived together with Osmundea pinnatifida, Gigartina pistillata and Phyllophora crispa from the sublittoral fringe. Delesseria sanguinea was probably to most intolerant since it was damaged at depths of 6m (Smith, 1968). Holt et al., (1995) suggested that Delesseria sanguinea is probably generally sensitive of chemical contamination. Although Laminaria hyperborea may be relatively insensitive to synthetic chemical pollution, evidence suggests that grazing gastropods, amphipods and red algae are sensitive. Loss of red algae is likely to reduce the species richness and diversity of the biotope and the understorey may become dominated by encrusting corallines; however, red algae are likely to recover relatively quickly.

Reduced oxygen concentrations have been shown to inhibit both photosynthesis and respiration in macroalgae (Kinne, 1977). Despite this, macroalgae are thought to buffer the environmental conditions of low oxygen, thereby acting as a refuge for organisms in oxygen depleted regions especially if the oxygen depletion is short-term (Frieder et al., 2012). A rapid recovery from a state of low oxygen is expected if the environmental conditions are transient. If levels do drop below 4 mg/l negative effects on these organisms can be expected with adverse effects occurring below 2 mg/l (Cole et al., 1999).

Sensitivity Assessment. Reduced oxygen levels are likely to inhibit photosynthesis and respiration but not cause a loss of the macroalgae population directly. However, small invertebrate epifauna may be lost, causing a reduction in species richness. Therefore a resistance of ‘High’ is recorded. Resilience is likely to be ‘High’, and the biotopes ‘Not sensitive’ at the benchmark level.

Johnston & Roberts (2009) conducted a meta-analysis, which reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected 6 marine habitats (including subtidal reefs). A 30-50% reduction in species diversity and richness was identified from all habitats exposed to the contaminant types. Johnston & Roberts (2009) however also highlighted that macroalgal communities are relatively tolerant to contamination, but that contaminated communities can have low diversity assemblages which are dominated by opportunistic and fast growing species (Johnston & Roberts, 2009 and references therein).

Holt et al. (1995) suggest that Laminaria hyperborea may be tolerant of nutrient enrichment since healthy populations are found at ends of sublittoral untreated sewage outfalls in the Isle of Man. Increased nutrient levels e.g. from sewage outfalls, has been associated with increases in abundance, primary biomass and Laminaria hyperborea stipe production but with concomitant decreases in species numbers and diversity (Fletcher, 1996).

Increased nutrients may result in phytoplankton blooms that increase turbidity. Increased nutrients may favour sea urchins, e.g. Echinus esculentus, due their ability to absorb dissolved organics, and result in increased grazing pressure leading to loss of understorey epiflora/fauna, decreased kelp recruitment and possibly 'urchin barrens'. Therefore, although nutrients may not affect kelps directly, indirect effects such as turbidity, siltation and competition may significantly affect the structure of the biotope.

However, this biotope is considered to be 'Not sensitive' at the pressure benchmark, that assumes compliance with good status as defined by the WFD.

Organic enrichment is associated with eutrophication, increased siltation and turbidity (Fletcher 1996). Eutrophication is associated with loss of perennial algae and replacement by mussels or opportunistic algae (Fletcher 1996). Johnston & Roberts (2009) conducted a meta-analysis, which reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected 6 marine habitats (including subtidal reefs). A 30-50% reduction in species diversity and richness was identified from all habitats exposed to the contaminant types. Johnston & Roberts (2009) also highlighted that macroalgal communities are relatively tolerant to contamination, but that contaminated communities can have low diversity assemblages which are dominated by opportunistic and fast growing species (Johnston & Roberts, 2009 and references therein).

Holt et al. (1995) suggest that Laminaria hyperborea may be tolerant of organic enrichment since healthy populations are found at ends of sublittoral untreated sewage outfalls in the Isle of Man. Increased nutrient levels e.g. from sewage outfalls, has been associated with increases in abundance, primary biomass and Laminaria hyperborea stipe production but with concomitant decreases in species numbers and diversity (Fletcher, 1996). Increases in ephemeral and opportunistic algae are associated with reduced numbers of perennial macrophytes (Fletcher, 1996). Increased nutrients may also result in phytoplankton blooms that increase turbidity. Therefore, although nutrients may not affect kelps directly, indirect effects such as turbidity may significantly affect the structure of IR.LIR.K.LhypLoch.

Sensitivity assessment. Resistance to the pressure is considered ‘Low’, and resilience ‘Medium’. The sensitivity of this biotope to organic enrichment is assessed as ‘Medium’.

Physical Pressures

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very Low’). Sensitivity within the direct spatial footprint of this pressure is, therefore ‘High’. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

If rock substrata were replaced with sedimentary substrata this would represent a fundamental change in habitat type, which Laminaria hyperborea would not be able to tolerate (Birket et al., 1998). The biotope would be lost.

Sensitivity assessment. Resistance to the pressure is considered “None”, and resilience “Very Low” or ‘None’. The sensitivity of this biotope to change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa is assessed as “High”.

Barradas et al. (2011) scraped all macro-algae from intertidal Portuguese rock pools, including the dominant canopy forming Laminaria ochroleuca and understory algae. l small (mean length 2.02cm) Laminaria ochroleuca recruits appeared 1 month following removal at a mean density of 40 recruits per m2. Four months after removal sporophytes had an average length of 14.91cm and an average density of 82 recruits per m2. Barradas et al. (2011) noted a lack of recruitment in natural adjacent Laminaria ochroleuca populations and theorized the rapid colonization of Laminaria ochroleuca was caused by latent microscopic spores on the underlying rock which grew rapidly when the Laminaria ochroleuca canopy was removed. Barradas et al. (2011) did not comment on the length of time for Laminaria ochroleuca to reach similar size and density to that of pre-treatment nor the likely environmental conditions which spores could tolerate and for how long, however, the results in Barradas et al. (2011) demonstrate Laminaria ochroleuca can recover from disturbance rapidly.

Christie et al. (1998) observed Laminaria hyperborea habitat regeneration following commercial Laminaria hyperborea trawling in south Norway. Within the study area, trawling removed all large canopy-forming adult Laminaria hyperborea. In 2-6 years of harvesting, a new canopy had formed 1m off the seabed. The associated holdfast communities recovered in 6 years, however, the epiphytic stipe community did not fully recover and may take up to 10 years to recover (Svendsen, 1972). Christie et al. (1998) suggested that kelp habitats were relatively resistant to direct disturbance/removal of Laminaria hyperborea canopy.

Recurrent disturbance occurring at a smaller time scale than the recovery period of 2-6 years (stated above) could extend recovery time. Kain (1975) cleared sublittoral blocks of Laminaria hyperborea at different times of the year for several years. The first colonizers and succession community differed between blocks and at what time of year the blocks were cleared however within 2 years of clearance the blocks were dominated by Laminaria hyperborea (Fletcher et al., 2006). Lienaas & Christie (1996) also observed Laminaria hyperborea re-colonization of “urchin barrens”, following removal of urchins. The substratum was initially colonized by filamentous macroalgae and Saccharina latissima however after 2-4 years Laminaria hyperborea dominated the community.

Sensitivity assessment. Abrasion due to passing bottom gear has the potential to remove a significant proportion of the standing kelp population, similar to direct harvesting. The resident red algal turf may also be affected by direct abrasion while fauna on vertical surfaces may avoid direct impact. Therefore, resistance in probably ‘Low’. Laminaria ochroleuca has been shown to recovery rapidly (within 1-2 years) following complete kelp canopy removal. Laminaria hyperborea has been shown can recover within 2-6 and the associated community 7->10 years (Birkett et al., 1998). The full community is, therefore, likely to completely recover in >2 years. Resilience is therefore probably ‘Medium’ and sensitivity has been assessed as ‘Medium’.

Suspended Particle Matter (SPM) concentration has a linear relationship with sub-surface light attenuation (Kd) (Devlin et al., 2008). An increase in SPM results in a decrease in sub-surface light attenuation. Light availability and water turbidity are principal factors in determining kelp depth range (Birkett et al., 1998). Light penetration influences the maximum depth at which kelp species can grow and it has been reported that laminarians grow down to depths at which the light levels are reduced to 1 percent of incident light at the surface. Maximal depth distribution of laminarians, therefore, varies from 100 m in the Mediterranean to only 6-7 m in the silt-laden German Bight. In Atlantic European waters, the depth limit is typically 35 m. In very turbid waters the depth at which Laminaria hyperborea is found may be reduced, or in some cases excluded completely (e.g. Severn Estuary), because of the alteration in light attenuation by suspended sediment (Birkett et al. 1998b; Lüning, 1990).

Laminaria spp. show a decrease of 50% photosynthetic activity when turbidity increases by 0.1/m (light attenuation coefficient =0.1-0.2/m; Staehr & Wernberg, 2009). An increase in water turbidity will likely affect the photosynthetic ability of Laminaria hyperborea and Laminaria ochroleuca and decrease Laminaria hyperborea abundance and density (see sub-biotope- IR.MIR.KR.Lhyp.Pk). Kain (1964) suggested that early Laminaria hyperborea gametophyte development could occur in the absence of light. Furthermore, observations from south Norway found that a pool of Laminaria hyperborea recruits could persist growing beneath Laminaria hyperborea canopies for several years, indicating that sporophyte growth can occur in light-limited environments (Christe et al., 1998). However in habitats exposed to high levels of suspended silts Laminaria hyperborea is out-competed by Saccharina latissima, a silt tolerant species, and thus, a decrease in water clarity is likely to decrease the abundance of Laminaria hyperborea in the affected area (Norton, 1978).

Díez et al., (2003) studied subtidal vegetation distribution patterns in relation to environmental conditions (pollution, wave exposure, sedimentation, substratum slope and depth) in northern Spain. The results showed that Laminaria ochroleuca only occurred at sites without sedimentation loading. In contrast to this evidence, IR.LIR.K.LhypLoch is found in low energy environments (Connor et al., 2004) which are inherently subject to a degree of siltation.

Sensitivity Assessment. An increase in water clarity from clear to intermediate (10-100 mg/l) represent a change in light attenuation of ca 0.67-6.7 Kd/m, and is likely to result in a greater than 50% reduction in photosynthesis of Laminaria spp. Therefore, the dominant kelp species will probably suffer a significant decline and resistance to this pressure is assessed as ‘Low’. Resilience to this pressure is probably ‘Medium’ at the benchmark. Hence, this biotope is assessed as having a sensitivity of ‘Medium ‘to this pressure.

Smothering by sediment (e.g. 5 cm of material) during a discrete event is unlikely to damage Laminaria hyperborea or Laminaria ochroleuca sporophytes but is likely to affect gametophyte survival as well as holdfast fauna, and interfere with zoospore settlement (Moy & Christie, 2012). Given the microscopic size of the gametophyte, 5 cm of sediment could be expected to significantly inhibit growth. However, laboratory studies showed that kelp gametophytes can survive in darkness for between 6-16 months at 8 °C and would probably survive smothering by a discrete event. Once returned to normal conditions the gametophytes resumed growth or maturation within one month (Dieck, 1993). Intolerance to this factor is likely to be higher during the peak periods of sporulation and/or spore settlement.

Díez et al., (2003) studied subtidal vegetation distribution patterns in relation to environmental conditions (pollution, wave exposure, sedimentation, substratum slope and depth) in northern Spain. The results showed that Laminaria ochroleuca only occurred at sites without sedimentation loading and may, therefore, be sensitive to light sedimentation. In contrast to this evidence IR.LIR.K.LhypLoch is found in low energy environments which are inherently subject to a degree of siltation.

If inundation is long lasting then the understory flora may be adversely affected. If clearance of deposited sediment occurs rapidly then understory communities are expected to recover quickly. In moderately exposed examples of IR.LIR.K.LhypLoch deposited sediment is unlikely to remain for more than a few tidal cycles (due to water flow or wave action). In wave sheltered examples of IR.LIR.K.LhypLoch sediment could remain and recovery rate would be related to sediment retention.

Sensitivity assessment. Resistance has been assessed as ‘Medium’, resilience as ‘High’. Sensitivity has been assessed as ‘Low’.

Smothering by sediment (e.g. 30 cm of fine material) in a discrete event is unlikely to damage Laminaria hyperborea or Laminaria ochroleuca plants but is likely to affect gametophyte survival as well as holdfast fauna, and interfere with zoospore settlement. Given the microscopic size of the gametophyte, 30 cm of sediment could be expected to significantly inhibit growth. However, laboratory studies showed that gametophytes can survive in darkness for between 6-16 months at 8°C and would probably survive smothering by a discrete event. Once returned to normal conditions the gametophytes resumed growth or maturation within 1 month (Dieck, 1993). Intolerance to this factor is likely to be higher during the peak periods of sporulation and/or spore settlement.

Díez et al. (2003) studied subtidal vegetation distribution patterns in relation to environmental conditions (pollution, wave exposure, sedimentation, substratum slope and depth) in northern Spain. The results showed that Laminaria ochroleuca only occurred at sites without sedimentation loading and may, therefore, be sensitive to light sedimentation. In contrast to this evidence IR.LIR.K.LhypLoch is found in low energy environments which are inherently subject to a degree of siltation.

If inundation is long lasting then the understory flora may be adversely affected, which is likely in wave sheltered environments. If clearance of deposited sediment occurs rapidly then understory communities are expected to recover quickly. In moderately exposed examples of IR.LIR.K.LhypLoch deposited sediments are unlikely to remain for more than a few tidal cycles (due to water flow or wave action). In wave sheltered examples of IR.LIR.K.LhypLoch sediment could remain and recovery rate would be related to sediment retention.

Sensitivity assessment. Resistance has been assessed as ‘Medium’, resilience as ‘Medium’. Sensitivity has been assessed as ‘Medium’.

Shading of the biotope (e.g. by construction of a pontoon, pier etc) could adversely affect the biotope in areas where the water clarity is also low, and tip the balance to shade tolerant species, resulting in the loss of the biotope directly within the shaded area, or a reduction in laminarian abundance from forest to park type biotopes.

Sensitivity assessment. Resistance is probably 'Low', with a 'Medium' resilience and a sensitivity of 'Medium', albeit with 'low' confidence due to the lack of direct evidence.

Not relevant. This pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit the dispersal of spores. But spore dispersal is not considered under the pressure definition and benchmark.

Undaria pinnatifida has received a large amount of research attention as a major Invasive Non-Indigenous Species (INIS) which could out-compete native UK kelp habitats (see Farrell & Fletcher, 2006; Thompson & Schiel, 2012, Brodie et al., 2014; Hieser et al., 2014). Undaria pinnatifida was first recorded in the UK in 1994 attached to a boat in the Hamble estuary (Fletcher & Manfredi, 1995) and has since spread to sheltered, typically man-made, habitats around the UK e.g. marinas (Farrell & Fletcher, 2006).

Undaria pinnatifida was first recorded in Plymouth Sound, UK in 2003 (NBN, 2015) subsequent surveys in 2011 have reported that Undaria pinnatifida is widespread throughout Plymouth Sound, colonizing rocky reef habitats. Where Undaria pinnatifida is present Heiser et al. (2014) observed a significant decline in the abundance of other Laminaria species, including Laminaria hyperborea.

In new Zealand, Thompson & Schiel (2012) observed that native fucoids could out-compete Undaria pinnatifida and re-dominate the substratum. However, Thompson & Schiel (2012) suggested the fucoid recovery of the substratum was partially due to an annual Undaria pinnatifida die back, which as noted by Heiser et al. (2014) did not occur in Plymouth sound, UK. Undaria pinnatifida was successfully eradicated on a sunken ship in Clatham Islands, New Zealand, by applying a heat treatment of 70 °C (see Wotton et al., 2004) however numerous other eradication attempts have failed, and as noted by Fletcher & Farrell, (1999) once established Undaria pinnatifida resists most attempts of long-term removal. The biotope is unlikely to recover until Undaria pinnatifida is fully removed from the habitat, which as stated above is unlikely to occur. Furthermore as observed by Farrell & Fletcher (2006) the wave sheltered environment which can define IR.LIR.K.LhypLoch may facilitate the establishment of Undaria pinnatifida.

Sensitivity assessment. Resistance to the pressure is considered ‘None’, and resilience ‘Very Low’. The sensitivity of this biotope to the introduction of microbial pathogens is assessed as ‘High’.

Galls on the blade of Laminaria hyperborea and spot disease are associated with the endophyte Streblonema sp. although the causal agent is unknown (bacteria, virus or endophyte). The resultant damage to the blade and stipe may increase losses in storms. The endophyte inhibits spore production and, therefore, recruitment and recoverability. However, no other evidence was found.

Sensitivity assessment. Resistance to the pressure is considered ‘Medium’, and resilience ‘High’. The sensitivity of this biotope to the introduction of microbial pathogens is assessed as ‘Low’.

Kelp trawling and abrasion have been found to cause 75% mortality of kelp beds (See abrasion pressure). Therefore, incidental removal of the kelp species within this biotope is likely to fundamentally change the character of this biotope.

Kelp species are key/characterizing species within this biotope. Removal of canopy-forming kelps has been shown to increase desiccation and mortality of the understory macroalgae community (Hawkins & Harkin, 1985). Laminaria hyperborea stipes also host a large array of epiphytic species (Birkett et al., 1998). This epiphytic community would also be lost from the biotope if a large proportion of the kelp biomass were removed.

Sensitivity assessment. Resistance to the pressure is considered ‘None’, and resilience ‘Medium’. The sensitivity of this biotope to damage to seabed surface features is assessed as ‘Medium’.

Kelp trawling and abrasion have been found to cause 75% mortality of kelp beds (See abrasion pressure). Therefore, incidental removal of the kelp species within this biotope is likely to fundamentally change the character of this biotope.

Kelp species are a key characterizing species within this biotope. Removal of canopy-forming kelps has been shown to increase desiccation and mortality of the understory macro-algae community (Hawkins & Harkin, 1985). Laminaria hyperborea stipes also host a large array of epiphytic species (Birkett et al., 1998). This epiphytic community would also be lost from the biotope if a large proportion of the kelp biomass were removed.

Sensitivity assessment. Resistance to the pressure is considered ‘None’, and resilience ‘Medium’. The sensitivity of this biotope to damage to seabed surface features is assessed as ‘Medium’.

Blight, A.J. & Thompson, R.C., 2008. Epibiont species richness varies between holdfasts of a northern and a southerly distributed kelp species. Journal of the Marine Biological Association of the United Kingdom, 88 (03), 469-475.

Bryan, G.W., 1984. Pollution due to heavy metals and their compounds. In Marine Ecology: A Comprehensive, Integrated Treatise on Life in the Oceans and Coastal Waters, vol. 5. Ocean Management, part 3, (ed. O. Kinne), pp.1289-1431. New York: John Wiley & Sons.

Erwin, D.G., Picton, B.E., Connor, D.W., Howson, C.M., Gilleece, P. & Bogues, M.J., 1990. Inshore Marine Life of Northern Ireland. Report of a survey carried out by the diving team of the Botany and Zoology Department of the Ulster Museum in fulfilment of a contract with Conservation Branch of the Department of the Environment (N.I.)., Ulster Museum, Belfast: HMSO.

Farrell, P. & Fletcher, R., 2006. An investigation of dispersal of the introduced brown alga Undaria pinnatifida (Harvey) Suringar and its competition with some species on the man-made structures of Torquay Marina (Devon, UK). Journal of Experimental Marine Biology and Ecology, 334 (2), 236-243.

Kitching, J., 1941. Studies in sublittoral ecology III. Laminaria forest on the west coast of Scotland; a study of zonation in relation to wave action and illumination. The Biological Bulletin, 80 (3), 324-337

Sivertsen, K., 1997. Geographic and environmental factors affecting the distribution of kelp beds and barren grounds and changes in biota associated with kelp reduction at sites along the Norwegian coast. Canadian Journal of Fisheries and Aquatic Sciences, 54, 2872-2887.

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